a) Field of the Invention
The present invention relates to a gradient index lens component which is suited for use as an image pickup lens component in electronic image pickup apparatuses such as video cameras and also to an image pickup apparatus using the gradient index lens component.
b) Description of the Prior Art
In recent years, now that electronic image pickup apparatuses are widely used in domestic video cameras, video telephones and door phones with cameras, it is important to develop a compact lens system which is usable in these electronic image pickup apparatuses and that can be manufactured at a low cost. The conventional lens systems which are used in these electronic image pickup apparatuses are generally composed of three to six lens elements. There are also known other lens systems which are composed of a single lens element for configuring the electronic image pickup apparatuses compactly and manufacturing them at low cost. An example of the conventional lens systems which is composed of a single lens element is disclosed in Japanese Patent Kokai Publication No. Hei 4-191716. This reference discloses a lens system which uses an aspherical surface. In regard to lens systems which are to be used for different purposes, Japanese Patent Kokai Publication No. Sho 60-91316 discloses a gradient index rod lens element having planar surfaces on both sides which is to be used as a collimator for a laser, Japanese Patent Kokai Publication No. Sho 50-11045 proposes a gradient index rod lens element having planar surfaces on both sides which is to be used as an optical fiber connector and Japanese Patent Kokai Publication No. Sho 60-140307 discloses a lens component composed of a single lens element having a concave surface on the object side and a planar surface on the image side which is to be used as an optical pickup and a collimator for lasers. Further, known as an objective lens system for endoscopes consisting of two lens elements is a lens system disclosed by Japanese Patent Kokai Publication No. Sho 52-29238 which is composed of a combination of a homogenous concave lens element and a gradient index lens element having planar surfaces on both sides.
Out of the conventional examples mentioned above, the lens system which is composed of the three to six lens elements has defects that it has high manufacturing cost due to the large number of lens elements and allows optical performance to be degraded due to assembling errors. Further, the lens system disclosed by Japanese Patent Kokai Publication No. Hei 4-191716, which is composed of the single lens element, has a defect that it produces curvature of field, distortion, and chromatic aberration in large amounts. Each of the gradient index lens elements which are disclosed by Japanese Patents Kokai Publication No. Sho 60-91316 and No. Sho 50-11045, which have planar surfaces on both sides, is configured for picking up monochromatic images and has optical performance mainly for axial rays, produces offaxial aberrations in large amounts, and does not take chromatic aberration into consideration. The lens system disclosed by Japanese Patent Kokai Publication No. Sho 60-140307, which is composed of a single gradient index lens element having a concave surface on the object side and a planar surface on the image side produces astigmatism in a large amount and does not take chromatic aberration into consideration. Furthermore, the lens system disclosed by Japanese Patent Kokai Publication No. Sho 52-29238, which is composed of two lens elements, has defects that it requires high manufacturing cost and that it produces chromatic aberration in a large amount.